Professional development and professional identity of English language teachers have usually been explored separately in the research agenda. However, there might be a nexus of relationships between professional identity and professional development in the context of English language teaching. This study, therefore, explored how professional identity might contribute to professional development of English language teachers. To this end, 60 English language teachers from inner, 60 from outer, and 60 from expanding circle of language use were sampled to fill in a questionnaire which was constructed and validated by the researchers. The study concluded that language teachers’ professional development could be theorized on a development of past-present-aspirational identity. It was also found that language teachers’ professional identity could be improved through development of interpersonal relations, system of knowledge and belief, and intrapersonal identity that would be considered as sub-identities of English language teachers’ professional identity.